1. Field of the Invention
The present invention relates to an apparatus to control the ratio of air to fuel of the air-fuel mixture which is applied to an internal combustion engine, and more particularly to an apparatus to control the ratio of air to fuel of air-fuel mixture through the control of the rate of air supplied to the main system fuel passage and the slow system fuel passage of a carburetor provided for supplying the air-fuel mixture to an internal combustion engine.
2. Description of the Prior Art
It is known to incorporate a catalytic converter having ternary catalytically active substances into the exhaust system of the internal combustion engine of an automobile in order to simultaneously reduce the components of exhaust gas which are injurious to health, such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). It is required to supply an air-fuel mixture of an air-fuel ratio corresponding to the stoichiometric air-fuel ratio into the cylinders of an internal combustion engine, since the maximum cleaning efficiency of the ternary catalytically active substances is attained when the exhaust gas is produced by the combustion of an air-fuel mixture of the stoichiometric air-fuel ratio. An air-fuel ratio controller to meet such a requirement is known, which includes a main system air-bleeding passage connected to the main system fuel passage connecting to the main jet of a carburetor, a slow system air-bleeding passage connected to the slow system fuel passage connecting to the slow system fuel supply port of the carburetor, and a main system electromagnetic control valve for controlling the main system air bleeder and a slow system electromagnetic control valve for controlling the slow system air bleeder, which are disposed within the main system air-bleeding passage and the slow system air-bleeding passage, respectively, and are adapted to be controlled by a control signal provided by converting the output signal of an oxygen sensor disposed within the exhaust passage of the engine by means of an electronic control unit. It is proposed to control the quantity of air to be supplied to the main system fuel passage and to the slow system fuel passage through the main system air-bleeding passage and through the slow system air-bleeding passage, respectively, with an air-fuel ratio controller as described above, so that the air-fuel ratio of the air-fuel mixture which is supplied into the cylinders of an engine is controlled so as to be close to the stoichiometric air-fuel ratio. However, such proposal as described above has a disadvantage in controlling the air-fuel ratio. In a carburetor, fuel is supplied through the slow system fuel supply port while not being supplied through the main nozzle when the throttle opening is small, whereas the fuel is supplied through both the slow system fuel supply port and the main nozzle, mainly through the main nozzle, when the throttle opening is large. When the throttle opening is large, the required air-bleeding quantity in the main system is less as compared with the required air-bleeding quantity in the slow system when the throttle opening is small. Nevertheless, the air-fuel ratio controller is provided with a main system electromagnetic control valve and a slow system electromagnetic control valve of the same flow rate characteristic. Accordingly, an excessive quantity of air is supplied through the main system air-bleeding passage due to delayed response of the electromagnetic valve when the throttle valve is suddenly opened. Consequently, an excessively lean air-fuel mixture is supplied temporarily into the cylinders of the engine, thus resulting in irregular acceleration.